GB802785A - Improvements in or relating to combined venting and overpressure release valves - Google Patents

Abstract

802,785. Pressure relieving devices for fluids; valves. NATIONAL PRESTO INDUSTRIES, Inc. July 1, 1955, No. 19147/55. Class 135. A combine venting and pressure relief valve for pressure cookers and similar pressure vessels comprises a spool member 14 mounted with clearance in an aperture 12 in the wall 10 of the pressure vessel and having upper and lower end flanges 18, 20 disposed outside and inside the vessel respectively, the flanges being spaced apart a distance greater than the thickness of the wall 10 to permit limited vertical movement of the spool member the lower flange of which is flexible so that the spool member may be ejected from the aperture when the pressure in the vessel exceeds a predetermined value. As shown in Fig. 1, the complete spool is made of a heat-resistant resilient material. The central portion 16 of the spool has projecting portions 22 adapted to engage the wall of the aperture 12 and intermediate portions 24. The top flange 18 has axially projecting portions 26 on its under side positioned opposite the projecting portions 22. The portions 26 are separated by recessed portions 28. Before heating commences, the upper flange 18 rests by the projecting portions 26 on the wall 10 and air may escape from the vessel past the portions 24, 28. As pressure develops in the vessel however the smooth top surface 30 of the lower flange 20 seals against the lower face of the wall 10 and remains so sealed until cooling starts or an excessive pressure arises in the vessel. Upon cooling the spool falls and air is admitted past the portions 24, 28 to destroy any vacuum in the vessel. In a modification the central portion 16 is formed with radical slots extending into the lower surface of the upper flange 18 and with a part spherical recess in its base. A metallic weight may be embedded in the spool member to ensure adequate venting of air. In another embodiment, Fig. 9, suitable for a vessel having a wall 61 of appreciable thickness, the spool 64 has a stem 66 of less diameter than a bore 62 in the wall 61 and the bore 62 has a counterbore 63 to receive the lower flange 70 of the spool. The natural irregularities in the lower surface of the upper flange 68 and the top of the wall 61 permit the egress and ingress of air. The spool 64 also has a central bore 71 in which is loosely accommodated the stem 76 of a metallic spool 74 having upper and lower flanges 78, 80 the lower flange being constituted as a weight and having a convex upper surface adapted to seal against the wall of a concave recess 72 in the spool. The natural irregularities in the surface of the flange 78 enable air to flow through bore 71 when the flange 78 is seated as shown. In a further modification, the spool A74 co-operates with a resilient annular disc arranged loosely between flanges in the cover or wall of the pressure vessel. U.S.A. Specification 2,429,149 is referred to.